From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id C4A646B004D for ; Tue, 9 Jun 2009 06:17:29 -0400 (EDT) Received: from m3.gw.fujitsu.co.jp ([10.0.50.73]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id n59AoW5J013207 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Tue, 9 Jun 2009 19:50:32 +0900 Received: from smail (m3 [127.0.0.1]) by outgoing.m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 3B15445DD7B for ; Tue, 9 Jun 2009 19:50:32 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 19D5045DD7E for ; Tue, 9 Jun 2009 19:50:32 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id EBE9F1DB8042 for ; Tue, 9 Jun 2009 19:50:31 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.249.87.107]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 7D89E1DB8038 for ; Tue, 9 Jun 2009 19:50:31 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA In-Reply-To: <20090609104404.GP18380@csn.ul.ie> References: <20090609185036.DD8E.A69D9226@jp.fujitsu.com> <20090609104404.GP18380@csn.ul.ie> Message-Id: <20090609194551.DD94.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Tue, 9 Jun 2009 19:50:30 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: kosaki.motohiro@jp.fujitsu.com, Rik van Riel , Christoph Lameter , yanmin.zhang@intel.com, Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML List-ID: > On Tue, Jun 09, 2009 at 06:59:03PM +0900, KOSAKI Motohiro wrote: > > > > > > Here it is just recording the jiffies value. The real smarts with the counter > > > > > > use time_before() which I assumed could handle jiffie wrap-arounds. Even > > > > > > if it doesn't, the consequence is that one scan will occur that could have > > > > > > been avoided around the time of the jiffie wraparound. The value will then > > > > > > be reset and it will be fine. > > > > > > > > > > time_before() assume two argument are enough nearly time. > > > > > if we use 32bit cpu and HZ=1000, about jiffies wraparound about one month. > > > > > > > > > > Then, > > > > > > > > > > 1. zone reclaim failure occur > > > > > 2. system works fine for one month > > > > > 3. jiffies wrap and time_before() makes mis-calculation. > > > > > > > > > > > > > And the scan occurs uselessly and zone_reclaim_failure gets set again. > > > > I believe the one useless scan is not significant enough to warrent dealing > > > > with jiffie wraparound. > > > > > > Thank you for kindful explanation. > > > I fully agreed. > > > > Bah, no, not agreed. > > simple last failure recording makes following scenario. > > > > > > 1. zone reclaim failure occur. update zone_reclaim_failure. > > ^ > > | time_before() return 1, and zone_reclaim() return immediately. > > v > > 2. after 32 second. > > ^ > > | time_before() return 0, and zone_reclaim() works normally > > v > > 3. after one month > > ^ > > | time_before() return 1, and zone_reclaim() return immediately. > > | although recent zone_reclaim() never failed. > > v > > 4. after more one month > > > > Pants. > > /me slaps self > > + /* Watch for jiffie wraparound */ > + if (unlikely(jiffies < zone->zone_reclaim_failure)) > + zone->zone_reclaim_failure = jiffies; > + > + /* Do not attempt a scan if scanning failed recently */ > + if (time_before(jiffies, > + zone->zone_reclaim_failure + zone_reclaim_interval)) > + return 0; > + > > ? looks good. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org